Hydrocarbon reserves are becoming increasingly difficult to locate and access, as the demand for energy grows globally. Typically, various technologies are utilized to collect measurement data and then to model the location of potential hydrocarbon accumulations. The modeling may include factors, such as (1) the generation and expulsion of liquid and/or gaseous hydrocarbons from a source rock, (2) migration of hydrocarbons to an accumulation in a reservoir rock, and/or (3) a trap and a seal to prevent significant leakage of hydrocarbons from the reservoir. The collection of these data may be beneficial in modeling potential locations for subsurface hydrocarbon accumulations.
At present, reflection seismic is the dominant technology for the identification of hydrocarbon accumulations. This technique has been successful in identifying structures that may host hydrocarbon accumulations, and may also be utilized to image the hydrocarbon fluids within subsurface accumulations. Typically, the body of water located above a subsurface region is ignored during processing of the seismic data, which focuses on the subsurface region. That is, the seismic processing is directed to identifying subsurface structures that may include hydrocarbons.
To determine the location of hydrocarbons, certain processes involve locating seepages from the seafloor, which are referred to as hydrocarbon seeps. These hydrocarbon seeps may result in bubble plumes in the water column, which may indicate the presence of an active hydrocarbon system. The identification of these bubble plumes is useful in assessing the exploration potential of a prospect. One method for detecting these bubble plumes uses high frequency sources and detectors in a device (e.g., a multi-beam echo sounder). This device can be tuned at close to the bubble resonance frequency and thus be effective at detecting these plumes. The high frequencies typically include 1 kilo Hertz and above. See, e.g., Leifer, I., R. Sassen, P. Stine, R. Mitchell, and N. Guinasso (2002), Transfer of hydrocarbons from natural seeps to the water column and atmosphere, Geofluids, 2(2), 95-107. However, as these techniques involve an additional expense, they are not always performed as part of an exploration site survey.
Lower frequency seismic data can be analyzed for evidence of water-column layering in a field known as “seismic oceanography.” See, e.g., Holbrook, W. S., P. Páramo, S. Pearse, and R. W. Schmitt (2003), Thermohaline Fine Structure in an Oceanographic Front from Seismic Reflection Profiling, Science, 301(5634), 821-824, and Ruddick, B., H. Song, C. Dong, and L. Pinheiro (2009), Water Column Seismic Images as Maps of Temperature Gradient, Oceanography, 22(1), 192-205. In this field, horizontal and nearly horizontal signals are produced by thermohaline (temperature/salinity) boundaries in the water column. These signals (along with residual layered source artifacts) constitute noise that can interfere with bubble-plume signals (i.e., the high-angle diffraction anomalies in the water layer). That is, the horizontal and sub-horizontal information may hinder identification of bubble-plume signals.
Given the existing technology, an enhancement to exploration techniques that enhance the ability to detect hydrocarbon seeps is needed. The proposed technique may provide a pre-drill technology that determines the presence and location of hydrocarbon seepages from the seafloor based on measured seismic data. Further, this method may be utilized to locate seafloor hydrocarbon seeps accurately and cost-effectively over the basin-to-play scale as a means to enhance basin assessment and to high-grade areas for exploration.
Additional background references may include John A. Hildebrand et al., “Seismic Imaging of the Water-Column Deep Layer Associated with the Deepwater Horizon Oil Spill”, Geophysics, Vol. 77, No. 2, pp. EN11-EN16, March 2012; Reeshidev Bansal et al., “Diffraction Enhancement in Prestack Seismic Data”, Geophysics, Vol. 70, No. 3, pp. V73-V79, May 2005; and Igor Kestemberg Marino et al., “Processing of High-Resolution, Shallow Seismic Profiles, Guanabara Bay—Rio de Janeiro State, Brazil”, Revista Brasileira de Geoffsica, Vol. 31, No. 4, pp. 579-594, 2013.